Alloys for high temperature use containing chromium, tungsten, nickel, cobalt



9, 1966 J. F. BALDWIN ETAL 1 3,265,494

ALLOYS FOR HIGH TEMPERATURE USE CONTAINING CHROMIUM, TUNGSTEN, NICKEL,COBALT Filed April 3, 1964 United States Patent ALLOYS FOR HIGHTEMPERATURE USE CON- TAINING CHROMIUM, TUNGSTEN, NICKEL,

COBALT James F. Baldwin, Locust Valley, N.Y., and Arthur T. Cape,Monterey, Calif., assignors to Coast Metals, Inc., Little Ferry, N..l.,a corporation of Delaware Filed Apr. 3, 1964, Ser. No. 357,124 2 Claims.(Cl. 75-171) This application is a continuation-in-part of applicationSerial No. 125,355 filed July 20, 1961, which was a continuation-in-partof application Serial No. 766,674 filed October 13, 1958, both of whichare now abandoned.

This invention relates generally to alloys for high temperature use,containing cobalt, chromium, tungsten and nickel as their principalconstituents.

In U.S. Patent No. 2,801,165, there is disclosed a cobalt-base alloywhich contains 18.75-23.25 tungsten, and 26-30% chromium, but which issubstantially free from nickel. This alloy has a short time tensilestrength, at 1800 F., of about 40,000 p.s.i.

In US. Patent No. 2,684,299, there is disclosed a cobalt-base alloycontaining 16-20% tungsten and 712% nickel, but this alloy, of which atypical example is the alloy commonly known as Haynes Stel-lite No. 36,has a maximum short time tensile strength, at 1800 F., of about 40,000p.s.i.

We have discovered, however, that by utilizing an alloy having acomposition within the following ranges, and provided that the ratio ofcobalt to chromium in the alloy is always at least 1.4:1, that the shorttime tensile strength of the alloy, at 1800" F., is increased to aminimum of 48,000 p.s.i.

If a maximum of chromium is used in the alloy, the minimum amount ofcobalt which can be used in the alloy, in order to maintain theaforesaid minimum ratio of cobalt to chromium, would be 42%. If theminimum amount of chromium is used in the alloy, the minimum amount ofcobalt which can be used in the alloy, in order to maintain theaforesaid minimum ratio of cobalt to chromium, would be 36.4%. As apractical matter, therefore, the cobalt range of such an alloy wouldvary from 36.4 to 42%, although the cobalt content could be increasedbeyond this range, depending upon the quantities of the otheringredients present in the alloy, principally the amounts of tungstenand nickel.

Moreover, it has been found that maximum values 7 as to short timetensile strength are maintained by decreasing the tungsten content ofthe alloy as the nickel content is increased.

The alloys of the aforesaid Patents 2,801,165 and 2,684,299, have, asalready stated, a short time tensile strength, at 1800 F., of about40,000 p.s.i. In contrast to this, the alloys of the present inventionhave a short time tensile strength, at 1800 F., of a minimum of 48,000p.s.i. This increase of at least 20% in the shout time tensile strengthis unusual in view of the relatively small amount of nickel in thealloy, and is probably due to the use of the relatively high chromiumcontent in conjunction "ice with the small amount of nickel. In anyevent, the difference in short time tensile strength is obviously adifference in degree rather than kind.

The nickel range of 4 to 6% is, however, extremely critical from anotherviewpoint, and that is, from the viewpoint of ductility or freedom frombrittleness of the alloy.

This may be explained by reference to the accompanying photomicrographs,in which FIG. 1 is .a photomicrograph, at a magnification of 270x, of analloy corresponding to the above-mentioned preferred alloy, butcontaining 10% nickel and 40% cobalt;

FIG. 2 is a photomicrograph, at a magnification of 270x, of an alloycorresponding to the above-mentioned preferred alloy, but containing 7%nickel and 43% cobalt; v

FIG. 3 is a photomicrograph, at a magnification of 270x, of an alloycorresponding to the preferred alloy, and

FIG. 4 is a photomicrograph, at a magnification of 270x, of an alloycorresponding to the preferred alloy, but containing 3% nickel and 47%cobalt.

Referring to FIG. 1, it will be seen that there is an excessive amountof a continuous black or dark phase, which is an acicular carbide, andwhich, although it supplies resistance to wear in the alloy, i highlydisadvantageous in that it is a source of brittleness in the alloy.

This brittleness, which makes the alloy undesirable both for hard facingpurposes and for making castings thereof, manifests itself in thefollowing rather dramatic manner. Weld rods made of the alloy werepassed through a centerless grinder for the purpose of grinding the rodsto make them suitable for purposes of welding. Due to the brittleness ofthe rods virtually all of the rods became shattered in the course oftheir passage through the centerless grinder.

Referring to FIG. 2, it will be seen that the black or dark phase of thealloy, while slightly less in amount, is still substantial andcontinuous, to the extent that this alloy was also brittle, and thegreat majority of rods of this analysis passed through the centerlessgrinder became shattered in the course of their passage through thegrinder.

Referring to FIG. 3, it will be seen that there is a dark phase which issubstantially less in area than the dark phase in FIGS. 1 and 2. Thisalloy was entirely free from brittleness, exhibited a high degree ofductility, and of the rods of this analysis were passed through thecenterless grinder without any sign of shattering.

Referring to FIG. 4, it will be seen that there is gray phase, similarin total area to the dark phase in FIG. 2, but in which a fineprecipitate is formed which causes an increase in hardness, which, inturn, causes the alloy as a whole to have less resistance to impact thanthe alloy of FIG. 3. Such an alloy, while ductile, is undesirable formanufacture into weld rod and castings, because of this increase inhardness and resulting brittleness.

The distinction between the alloys of FIGS. 1, 2, 3 and 4 were furtheremphasized in testing the alloys with a Knoop indenter, using a 200 gm.load. The difference in Knoop values appears in the following table:

Alloy: Knoop value FIG. 1 535 FIG. 2 738 FIG. 3 678 FIG. 4 704 3 low.With 7% nickel, the Knoop value was too high. With 5% nickel, the Knoopvalue was at an optimum. With 3% nickel, the Knoop value rose to anundesirable point. The indication, therefore, was that the desired rangeof nickel in the alloy extends from a point somewhat below 7% to a.point somewhat above 3%.

Based on all of the foregoing tests and results, it was concluded thatoptimum results, from the standpoint of a combination of ductility(freedom from brittleness), and wear resistance, were obtained in therather narrow and critical range of 4 to 6% nickel.

In application, Serial No. 766,674, examples of alloys were disclosedcontaining in excess of about 6% nickel, specifically, nickel in amountsof 10%, and it was stated that these alloys had short time tensilestrengths of about 54,000 psi. However, as apparent from the foregoingphotomicrog-raphs and the tests described relative thereto, the alloysin Serial No. 766,674, containing 10% nickel, would not be suitable formanufacture into weld rods or for castings and would be entirelyunsatisfactory for hard facing purposes, due to their brittleness orlack of ductility.

The alloys of the present invention are particularly useful for thejoining areas of Waspalloy jet engine turbine blades, where constanthammering takes place at the joining areas of the interlocking blades.It is obvious that any brittleness in the alloy would render it entirelyunsatisfactory for this purpose.

It may be further pointed out that in application, Serial No. 766,674,it was stated that in order to obtain high strengths with ductility, andavoid brittleness in the alloy, it was necessary to decrease the nickelas the chromium content increased. In the examples, wherein the nickelcontent was 10%, the chromium content was 19%, or far below the 26-30%range of chromium in the alloy of the present invention. The alloy ofthe present invention is accordingly distinguished from the alloy ofPatent No. 2,684,299, not only in its high chromium range, but in itsnarrow and critical nickel range.

Having thus described our invention, we claim:

1. An alloy especially adapted for use as a welding material at hightemperatures, said alloy consisting of carbon 0.7 to 1.0%, chromium 26to 30%, tungsten 18 to 21%, nickel 4 to 6%, boron 0.005 to 0.1%, 0 to 1%silicon, 0 to 1% manganese, 0 to 3% iron, 0.75 to 1.25% vanadium, andthe balance being essentially all cobalt, and the ratio of cobalt tochromium being always at least 1.4 to 1, said alloy having a ductilityand freedom from brittleness such that rods of said alloy may be passedthrough a centerless grinder without the shattering of any substantialpercentage thereof.

2. An alloy especially adapted for use as a welding material at hightemperatures, said alloy consisting of about 0.85% carbon, about 28%chromium, about 19.5% tungsten, about 5% nickel, about .05% boron, about0.2% silicon, about 0.1% manganese, about .9% vanadium, about .4% iron,and about cobalt, said alloy having a ductility and freedom frombrittleness such that rods of said alloy may be passed through acenterless grinder Without the shattering of any substantial percentagethereof.

References Cited by the Examiner UNITED STATES PATENTS 7/1954 Binder 1717/1957 Baldwin et a1. 75-171

1. AN ALLOY ESPECIALLY ADAPTED FOR USE AS A WELDING MATERIAL AT HIGHTEMPERATURES, SAID ALLOY CONSISTING OF CARBON 0.7 TO 1.0%, CHROMIUM 26TO 30%, TUNGSTEN 18 TO 21%, NICKEL 4 TO 6%, BORON 0.005 TO 0.1%, 0 TO 1%SILICON, 0 TO 1% MANGANESE, 0 TO 3% IRON, 0.75 TO 1.25% VANADIUM, ANDTHE BALANCE BEING ESSENTIALLY ALL COBALT, AND THE RATIO OF COBALT TOCHROMIUM BEING ALWAYS AT LEAST 1.4 TO 1, SAID ALLOY HAVING A DUCTILITYAND FREEDOM FROM BRITTLENESS SUCH THAT RODS OF SAID ALLOY MAY BE PASSEDTHROUGH A CENTERLESS GRINDER WITHOUT THE SHATTERING OF ANY SUBSTANTIALPERCENTAGE THEREOF.